1. Technical Field
The present invention relates to a liquid crystal device that uses a liquid crystal with bend alignment and splay alignment as an alignment state, a method of driving the liquid crystal device and an electronic apparatus.
2. Related Art
A liquid crystal device that performs display using a liquid crystal varying its transmittance ratio is widely used as a display device of an electronic apparatus, such as an information processing device, a television, or a cellular phone. In the liquid crystal device, pixel electrodes are formed at positions corresponding to intersections of scanning lines that extend in a row direction and data lines that extend in a column direction. In addition, a pixel switch, such as a thin-film transistor (hereinafter, referred to as TFT, where appropriate), that turns on/off on the basis of a scanning signal supplied to a corresponding one of the scanning lines is provided at each of the intersections and interposed between each of the pixel electrodes and a corresponding one of the data lines. Furthermore, an opposite electrode is provided so as to be opposed to the pixel electrodes via the liquid crystal. An alignment state of the liquid crystal varies on the basis of a voltage applied between the pixel electrodes and the opposite electrode. In this manner, the amount of light transmitted in each of pixels is varied, thus making it possible to perform a predetermined display.
An Optical Compensated Bend (OCB) mode liquid crystal, which has been progressively developed in recent years as a new display mode for a liquid crystal device, has two types of alignment states, that is, a splay alignment and a bend alignment. The bend alignment is suitable for image display and is able to respond at a speed higher than an existing Twisted Nematic (TN) liquid crystal. When an initial state, that is, a state where an applied voltage is 0 V, has been continued for a long time, the OCB liquid crystal is placed in the splay alignment that is not suitable for image display. Therefore, when an image is displayed, it is necessary to perform an initial transition operation when power is on, or the like, to transfer liquid crystal molecules to the bend alignment. The transition from the splay alignment to the bend alignment in the initial transition operation is performed by applying a high voltage for a certain period of time.
Even when the transition from the splay alignment to the bend alignment is once performed through the initial transition operation, if a voltage of a predetermined level or above is not applied for some time, the OCB liquid crystal cannot maintain the bend alignment and returns from the bend alignment to the splay alignment. This phenomenon is called reverse transition. JP-A-2003-279931 (particularly, at paragraph [0016], or the like) describes that, in order to suppress the occurrence of reverse transition, a pulse voltage corresponding to non-image data is applied during one frame period. In a normally white OCB liquid crystal, the state where a pulse voltage is applied corresponds to black display, so that applying a pulse voltage to maintain the bend alignment is also called black insertion. JP-A-2003-279931 also describes that there is a correlation between a pulse voltage value that is applied in black insertion and the effect of maintaining the bend alignment.
In the meantime, in regard to the OCB liquid crystal, JP-A-2003-202549; (particularly, in FIG. 14) describes the voltage-transmittance ratio characteristics of an OCB liquid crystal element. In this voltage-transmittance ratio characteristics, as an applied voltage increases, the transmittance ratio decreases. However, when the voltage exceeds a voltage that corresponds to a so-called black level, the transmittance ratio increases, on the contrary.
As described in JP-A-2003-279931, when black insertion is performed, there is a correlation between the pulse voltage value and the effect of maintaining the bend alignment, and the effect of maintaining the bend alignment is enhanced by inserting a higher voltage pulse. For this reason, in order to improve reliability of maintaining the bend alignment, it is desirable that a voltage as high as possible is applied for black insertion.
On the other hand, when a high voltage that exceeds a black level is applied, the transmittance ratio increases as described in JP-A-2003-202549 and, as a result, light leakage occurs in black insertion. Because this light leakage is originally unnecessary for display, there is a possibility that the display characteristics of the OCB liquid crystal may be adversely affected. Thus, it is not easy to improve reliability of maintaining the bend alignment while avoiding adversely affecting the display characteristics.